1. Field of the Invention.
The present invention relates to apparatus for detecting when energy is being reflected from a specular surface and for inhibiting signals from the detectors when the reflection is specular.
2. Description of the Prior Art.
In my U.S. Pat. No. 4,716,430, I describe a pulse proximity detection system wherein a light emitting diode sends a pulsed beam of energy to a remote surface for reflection therefrom. A pair of detectors which are spaced from the remote surface by different distances receive the reflections and produce electrical signals in accordance with the amount of energy they receive. The difference in magnitude of these signals is a function of the distance to the remote surface, and in my patent I determine this difference by taking the signal from the two detectors and releasing them through a pair of RC circuits whose resistance and capacitance values are set so that the signals are allowed to decay at different rates. Since the detector which is closest to the surface will have a larger signal built up thereon, the RC circuit with which it is associated is allowed to decay faster than the other detector. Accordingly, at some time after the signals are released to the RC circuits, for example by sample-and-hold circuits used in my patent, the signals will have decayed to the same value. A comparator determines when this time has occurred and produces an output accordingly. The length of time is dependent upon the difference in the magnitudes of the signals and accordingly is indicative of the distance to the remote surface. A somewhat similar system is disclosed in U.S. Pat. No. 3,937,574 wherein instead of using a time decay, the output of one detector is divided by the difference between the outputs of the two detectors to obtain a signal indicative of the distance to the remote surface.
As explained in my U.S. Pat. No. 4,716,430, the surface should be at least partly diffuse so that reflected energy from the spot upon which the LED directs the energy comes off at various angles which would not be the case if the surface were very highly specular. As a matter of fact, if a highly specular surface were encountered, the reflections back from the surface would be such that the output of the detectors would likely be erroneous and the calculation of the distance to the remote surface in error.
It is therefore desirable to determine when a specular surface is encountered and, when so encountered to inhibit any signals from the detectors from that surface so that an erroneous signal indicative of range is not produced. Erroneous range signals may be a significant problem with respect to some apparatus utilizing the circuitry of my patent. For example, in robotics, the circuitry may be used to determine the distance to objects which a robot moving around the area wishes to avoid. If false signals are encountered and not inhibited, the robot might collide with such objects or otherwise cause harm to its system operation.